<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script type="text/javascript">
			//只声明 没有赋值 现在num的值是undefined
			var num;
			num = 3.14;
			console.log(num);
			//typeof()判断变量的类型
			console.log(typeof(num));
		</script>
	</head>
	<body>
	</body>
</html>
